Potentiometric measurements are commonly utilized in chemical, biophysical and biochemical studies to determine hydrogen ion concentrations (pH), specific ion concentrations, and measurements of redox potentials in a media that may, or does contain biological material. Prior techniques for measurements include using glass electrodes and redox measurements with metal electrodes. There is a great interest in miniaturizing of devices for sensitive and reliable measurements of biologically significant parameters, and in increasing the accuracy of measurements while utilizing smaller amounts of sampling media exposed to the detecting apparatus.
In Thundat et al., U.S. Pat. No. 5,719,324, a piezoelectric transducer is disclosed that is fabricated with a cantilever having a spring element treated with a chemical having an affinity for a specific vapor phase chemical. An oscillator means maintains a resonant vibrational frequency during detection of a chemical, with changes in resonant frequency indicating amounts of targeted chemical detected in the monitored atmosphere.
In Wachter et al., U.S. Pat. No. 5,445,008, a mass microsensor is disclosed that is fabricated with a microcantilever having a chemical coating, the cantilever is oscillated by a piezoelectric transducer, the chemical coating on the microcantilever absorbs a targeted chemical from the monitored atmosphere. The resonant frequency of the microcantilever is analyzed to determine changes that indicate the amount of targeted chemical that is within the monitored atmosphere.
In Marcus et al., U.S. Pat. No. 5,475,318, a microprobe is disclosed that includes a microcantilever, a base, a probe tip projecting from the base, and a heating element that heats the probe tip, which comes into contact with a material to be investigated.
In Hafeman, U.S. Pat. No. 4,963,815, a device and method is provided for determining an analyte by measuring a redox potential-modulated photoinducing electrical signal from an electronically conducting layer on a semiconductor device.
In Kolesar, U.S. Pat. No. 4,549,427, a chemical nerve agent detector is disclosed that includes a transducer having two microcantilever oscillators. The active of two microcantilevers have a chemically selective substance that absorbs chemical nerve agents from the atmosphere, with modifications in the oscillation of the active microcantilever, and comparisons allowed between the frequency of the active cantilever and the reference cantilever.
The prior art obtained pH measurements with glass electrodes and redox measurements are accomplished with metal electrodes. Both of these techniques involve measuring very small potential changes and require high input impedance devices. One device utilized is the chemically sensitive field effect transistor in which the gate region of a transistor is made sensitive to chemical events through their effect on the gate potential. A similar device called a light addressable potentiometric semiconductor sensor has been utilized for biochemical process sensing by detecting potentiometric sensing through changes in pH, redox potential, or transmembrane potential. All of the above described methods and devices utilize electrical means for potentiometric sensing for detection and measuring of biologically significant parameters such as pH, redox potential, and ion concentrations of selective ions with limited sensitivities in relatively large sample volumes. Miniaturization is difficult using the prior art methods and devices. Thus there exists room for improvement within the art.